Processes fob preventing corrosion



Reiuued -May 9, 1950 PATENT OFFICE PROCESSES FOR PREVENTING CORROSIONAND CORROSION INHIBITORS Charles M. Blair, Jr., and William F. Gross,Webster Groves,

Mo., assignors to Petrolite Corporation, Ltd.-, Wilmington, DeL, acorporation of Delaware No Drawing. Original No. 2,468,163, dated April26, 1949', Serial No. 1,656, January 10, 1948. Application for reissueMarch 3, 1950, Serial 11 Claims.

(01. ass-ass) Matter enclosed in heavy brackets I: ppears in theoriginal patent but forms no part of this reissue specification; matterprinted initalics indicates the additions made by reissue This inventionrelates to the inhibition of corrosion 01' metals, and particularly to acomposition for use in preventing corrosion of metals and particularlyiron, steel, and ferrous alloys. The corrosion inhibitors contemplatedherein iind special utility in the prevention of corrosion of pipe orequipment which is in contact with a corrosive oil-containing medium,as, for example, in oil wells producing corrosive oil or oil-brinemixtures, in refineries, and the like. Our inhibitors may, however, beused in other systems or applications. They appear to possess prop-,

erties which impart to metals resistance to attack by a variety ofcorrosive agents, such as brines, weak inorganic acids, organic acids,CO2, ms, etc.

Compounds which we have found to be effective for the purpose describedabove be1ong to the general class of cyclic amidines, and in particularare substituted imidazolines, in which the imidazoline molecule containsat least one aliphatic, or cycloaliphatic hydrocarbon group containingfrom 8 to 32 carbon atoms. Cyclic imidazolines in which the 2-carbonatom is substituted by a long chain aliphatic hydrocarbon group areparticularly easy to prepare and are very effective for the present use.However, it has been found that equally effective compounds, it

' not somewhat more effective in some instances,

result when the aliphatic hydrocarbon group occurs as a substituent ofone of the nitrogen atoms, or of a relatively small organic radicalattached to one of the nitrogen atoms.

An important class of the reagents herein contemplated as corrosionpreventives may be represented by the following general formula:

in which either It or X, or both, contain or consist of an aliphatic orcycloaliphatic radical containing from 8 to 32 carbon atoms.

In the most general classification of reagents suitable for our process,the symbol x ma 111-- clude another imidazoline ring, as described morefully below. Shown in the most generalway, the

compounds contemplated for use herein may be represented by thefollowing formula:

Where n is the numeral 1 to 6 and R is hydrogen or an aliphatic orcycloaliphatic hydrocarbon radical.

In the simplest case, the group R' may be directly attached to thel-nitrogen atom of the 40 ring. as follows:

sans? We have found that particularly outstanding corrosion-preventivereagents result when the imidazoline compound contains basic nitrogengroups in addition to those inherently present in the imidazoline ring.In general, compounds of this type which are effective are those inwhich the basic nitrogen group is contained in the radical D in theabove formula. I

In this case the products may be represented by the formula:

N-CHI taining amino groups. The group R may be, and

usually is, an amino nitrogen substituent. Eiramples of organic radicalswhich Y-R. may

. represent are:

where R and R have their previous significance. Of this class ofreagents in which an amino group occurs as a portion of the l-nitrogensubstituent, those which are derived, at least theoretically, from thepolyethylene polyamines appear to be particularly effective as corrosioninhibitors and are so outstanding as to constitute an invention withinan invention. These have the general formula:

N-C Ha where R and R have their previous meanings,

and m is a small number, usually less than 6.

The preparation of an imidazoline substituted in the 2-position byaliphatic hydrocarbon radicals is well described in the literature andis readily carried out by reaction between a monocarboxylic acid and adiamine, or polyamine, containing at least one primary amino group, andat least one secondary amino group, or another primary amino groupseparated from the first primary amino group by two carbon atoms.Examples of suitable polyamines which can be em:

ployed for this conventional imidazoline synthesis max Bockmuhl et al.;U. s. No. 2,155,877, dated Apr. 25, 1939, Edmund Waldmann et al.; and U.S.- No. 2,155,878, dated Apr. 25, 1939, Edmund Waldmann et al. Also seeChem. Rev., 32,47 (43).

When'a'n aliphatic or cycloaliphatic carboxylic acid containing 9 ormore carbon atoms is employed in the above described synthesis, theresulting imidazoline will contain a2-substituent consisting of analiphatic hydrocarbon radical containing 8 or more carbon atoms.Suitable corrosion-preventive reagents may, therefore, be made directlyby reaction of acids such as oleic acid, linoleic acid, linolenic acid,erucic acid, talloil fatty acids, naphthenic acids, nonoic acid,

and the like, with suitable amines such as those enumerated above. Whenthis condensation is carried out at a temperature of 250 C. or higher,between equal mole proportions of mono-earboxylic acid and polyamine,two moles of water are evolved and the desired imidazoline is formed in1 almost quantitative yield. Such suitable reagents ma be represented bythe following formula:

Q i mom radical having from 8 to 32 carbon atoms. In the above formulasfor imidazolines it should be pointed out that where X is a hydrogenatom, the nitrogen atoms become equivalent, insofar as reaction isconcerned, and cannot be distinguished from one another. This issupposed, on theoretical grounds, to result from th mobility of thehydrogen proton, and its ease of transfer from one nitrogen atom to theother. However, where X is an organic substituent other than hydrogen,the nitrogen atoms are no longer equivalent. For the purpose of thepresent application, the nitrogen atom to which the radical X isattached will be called the l-nitrogen atom of the imidazoline ring.This is in conformance with the usual chemical convention in numberingheterocyclic ring positions. 4

As mentioned above, we have discovered that equally suitablecorrosion-preventive reagents may be obtained by introducing into theimidazoline compound an aliphatic hydrocargon group of proper size as aportion of the substituent attached to the l-nitrogen atom of theimidazoline ring. Where the aliphatic hydrocarbon group occurs in thisposition, it is unnecessary that the 2-carbon atom substituent contains8 or more carbon atoms. It may be, in fact, only a hydrogen atom or amethyl group, ethyl group, phenyl group, or other relatively smallhydrocarbon group, although it is not restricted to such small groups.The preparation of mmazoline compounds in which the higher molecularweight hydrocarbon radical occurs as a portion of the nitrogen atomsubstituent, are also readily prepared by methods analogous to thosealready described. In this case, however, a number of alternativeprocedures are possible. For example, one may prepare 2-methyl,l-(octadecylaminoethyl-) imidazoline by reaction of octadecylaminoethylethylenediamine with acetic acid at a temperature of 250 to300 C. until two moles of ease? I water are evolved for every mole oiacetic acid employed. The same reagent may result b the preparation oiz-methyl, l-aminoethyl imidaso line followed by alkylation withoctadecyl bromide and separation 01' resulting alkylamn products toisolate the desired product. For the preparation oi 1,2-substitutedimidazolines, see

King ll McMillan, J. A. C. S. 68, 1774 (1948); I

Kyrides et aL, J. Organic Chem. 12, 5'17 (1941).

Examples of suitable substituted imidazolines in which the aliphatic orcycloaliphatic group containing from 8 to 32 carbon atoms is a2-position substitucnt. are as follows:

-sin.

Z-undecylimida'soline NOH1 min.

2-hepiadeeyiimiduoline (8) N-OK I I CuBsnO \w-(Lm I II Z-pentadecyl,I-heptylimiduolins lN-CH: IHmO 013401! fl-octyl,l-hydroxyethylimiduolino N-OH:

. ioHsi 2-nonyl, l-decylimidasoline /NCH: c ms 2oleylimidnzoline (7N-OH;

C oHn. C sHA. C

H: 2-cyclohexylethyl, 1-methylimidasoline Neln.

ermo 01m 2-ebietyl, l-ethyloxyethyiimidasoline Suitable substitutedlmidazolines in which the aliphatic or cycloaliphatic groupcontainingirom 8 I to flcerbon atoms is the i-position substituent or isa part of this substituent, are exemplified by the iollowing:

N-CH:

7 l-oetadesyllmidszoiine (2) V N-OIIg sKn 2-methyl, l-oetylimi'dasolineN-cH,

OHOHaC N- H, V (unmounldodcqloxymethyl, z-hydroxymetliylimiduolino 4N-om creme l ('JgEOOGuHn l-oleoloxyethyl, 2-chloromethylimiduoline N-OHIcimo v sHaNILOnHn I-N-decylsminoetbyl, 2-ethylimidasoline /N--CH| cumIf- Hi CnHu l-abietyl, 2-phenylimidazoline We have pointed out abovethat imidazolines containing basic nitrogen groups, in addition to thoseoccurring in the imidazoline ring are particularly efiective corrosioninhibitors. Such products are readily prepared from the commereiallyavailable polyethylene polyamines, or from polyamines in which there arethree or more amino groups and in which there is at least one primaryamino group separated by two carbon atoms from a secondary or primaryamino group. Examples of suitable preferred compounds of this type arethe following:

/N-C H: CnHu- N H: IELNH] 2-heptadecyl, l-nminoethylimldazoline /N--UH2nHu-C iHi.NH.C:H .NH| Z-heptadecyl, l-diethylenediaminoi'midssolineN-CH:

08;.0 4 r JhHaNEOaHaNHfluHa Z-methyLI-bEAGOCIllIIIlhOQtChIll-HIIIIOQHIYMMIOUDQ I aKeNEOuEnl-dodeeylaminopropylimidasol'ine Nlm i oi'mNaoimoodounul-stcaroyloxyethylaminoethylimiduolinc N-CH:

1- N dode h drox ethynunlnoethylsham, i

N-OHI N H: I |H|.NH.CIH4NHO C .C Hu

1-stearamidoethylaininoethylimidazoliue Chloroparaflin alkylationproduct of l-aminoethyl,

2-methylimidazoline Although we have shown above the composition of anumber 0! eilectlve inhibitors which are' 'imldazolin'es containing atleast one aliphatic or cycloaliphatic hydrocarbon radical having from ato 32 carbon atoms, we should like to point out that, in general, themost efl'ective reagents and those having the most desirable solubilitycharacteristics are those in which the aliphatic or cycloaliphatic groupcontains from 10 to carbon atoms. Examples of such preferred groups aredecyl, oleyl, abietyl, stearyl, and the like.

The corrosion preventive products of the present invention, since theycontain an imidazoline ring, may, in general; be alkylated to formeither a l-alkvl-substituted Lnidazoline, or a quaternary ammonium salt,where the alkyl group is attached to either or both the 1 and 3nitrogenatoms; For example.- using :oetylr bromide as atypicalalkylating agent, the following reactions may becarried 'out:

. .(14) one-m 1- 11.0

H: I N- H:

\N- Hg 3 19m ns and 014K- Br OuHu Instead of the cetyl bromide used inthe examples above, one may use other alkylating agents such -i0=asmethyl bromide, benzyl chloride, ethyl sulfate, dichloroethyl ether,chloroparaflln, etc., to obtain equally suitable derivatives ofimidazolines which 'may be employed in the present process.

For details of preparation of various imidazolinium salts, such as thosementioned above, see, for example, Shepard and Bhonle, J. A. C. S. 69,2269 (1947).

Although we have described the corrosion inso hibitors or our process asimidazolines, we may,

in many instances, employ these compounds in the form of their salts,either with organic or inorganic acids. Being relatively strong bases,the imidazolines readily form such salts, and

' where the reagent contains basic groups in addition to the imidazolinering nitrogen atoms, they may form dior polysalts. Examples of acidswhich may be used to form such salts are hydrochloric acid, sulfuricacid, acetic acid,

0" oxalic acid, maleic acid, oleic acid, abietic acid,

phosphoric acid, petroleum sulphonic acid, naphthenic acid, rosin,phenylacetic acid, benzoic acid, and the like. Salts of theimidazolines, such as those above as described, appear to be equally asefiective as the free bases. Probably, in the dilute solutions in whichthey are employed as corrosion inhibitors, the salts hydrolyze orotherwise decompose to some extent and reach air-equilibrium with theacids and other constituents of the corrosion medium.

While we have. describedour corrosion in-. hibitors as imidazolines andhave illustrated them above as single ring compounds, it should 76 bepointed out that in some instances reagent a carboxylic acid at asuitable high temperature.

a diimidazoline is obtained.

HIN.CIHI.NH.CIH|.NH.C:H4.NH:

' Triethylenetetramine N C lI ILCOOII omooon 0,111.54)

Btcaric acid Acetic acid bH: I 1 NCH1 omo Tetraethylenepentamine NCH|CnHuCOOH CHr.COOH C11H-1LC Stearic acid Acetic acid 1 :H4 13m (3H4fi-CH: CHLC\ N- H:

Such diimidazolines are intendedv to be included when reference is ,madeto substituted imidazolines herein or in the claims.

Many obvious simple derivatives of the herein described corrosioninhibitors may be prepared which are also effective. For example, wehave deiined the groups R and R in the structural formulae above asbeing members of the class consisting of hydrogen, aliphatic, andcycloaliphatic hydrocarbon groups. Actually, theuse of halogenatedhydrocarbon groups appears to yield equally effective reagents, andchlorohydrocarbon groups, particularly, are readily introduced duringsynthesis. Since the chlorine atoms in these groups are relativelynon-reactive and yield productswith solubilities similar to thehydrocarbon derivative, they do not differ greatly in behavior from thecorrespondinghydrocarbon derivative.

Imidazolines containing a, relatively high molecular weight hydrocarbonradical, and substituted in the 4- and/or 5-ring positions are alsoeffective inhibitors, but are not so readily prepared from presentlyavailable commercial reagents.v

The method of carrying out our process is rela tively simple inprinciple. The corrosion preventive reagent is dissolved in the liquidcorrosive medium in small amounts and is thus kept in contact with themetal surface to be protected. Alternatively, the corrosion inhibitormay be applied first to the metal surface, either as is, or as asothenu'eacts this further with another mole of acids andthe like- Forthe protection of such wells, the reagent, either'undiluted or dissolvedin a suitable solvent, is fed down the annulus of the 'well between thecasing and producing tubing where it becomescomrnmgled with the fluid mthe well and is pumped or flowed from the ,well with these fluids, thuscontacting the inner wall or the casing, the outer and inner wall oftubing, and the inner surface of all wellhead flttings, connections'andnew lines handling the corrosive fluid.

Where the inhibitor, composition is a liquid, it is conventionally fedinto the well annulus by means or a motor driven chemical im'ector pump,

or it may be dumped periodically (e. g., once every day or two) into theannulus by means of a socalled ,fbOlI weev' device or similararrangement. Where-the inhibitor is a solid, it may be dropped into thewell as a solid lump or stick, it may be blown in as a powder withgas,or it may be washed in with a small stream of the well fluids or otherliquid. Where there is gas pressure on the casing, it is necessary, orcourse, to employ any of these treating metnods through a pressureequalizing chamber equipped to allow introduction of reagent into thechamber, equalization of pressure between chamber and casing, and travelof reagent from chamber to well casing. I

Occasionally, oil and gas wells are completed in such a manner thatthere is no opening between the annulus and the bottom of the tubing orpump. The results, for example, when the tubing'is surrounding at somepoint by a packing held by the casing or earth formation below thecasing. In such wells the reagent may be introduced into the tubingthrough a pressure equalizing vessel, after stopping the flow of fluids.After being so treated, the well should be left closed in for a periodof time suflicient to permit the reagent to drop to the bottom of thewell.

For injection into the well annulus, the corrosion inhibitor is usuallyemployed as a solution in a suitable solvent, such as mineral oil,methylethyl ketone, xylene, kerosene, or even water.

The selection of solvent will depend much upon use of solid sticks" orplugs of inhibitor is espelution in some carrier liquid or paste.Continuous application, as in the corrosive solution, is the preferredmethod, however.

The present process finds particular utility in the protection of metalequipment of oil and gas wells, especially those containing or producingcially convenient. These may be prepared by blending the inhibitor witha mineral wax, asphalt or resin in a proportion suflicient to give amoderately hard and high-melting solid which can be handled and fed intothe well conveniently.-

The amount of corrosion preventive agent required in our process varieswith the corrosiveness of the system, but where a continuous orsemi-continuous treating procedure is carried out as described above,the addition of reagent in the proportion of from one part per 1,000 toone part per 20,000 or more parts of corrosive fluid will generallyprovide protection. As an example of treating procedure and results, thefollowing actual well treatmenthistory is presented.

Treatment was made of a West Texas oil well producing 15 bbls. of oiland 1 bbl. of brine per day. The brine contained 2.75% chlorides asNaCl, and 275 parts per million of hydrogen sulflde. A solution ofZ-heptadecylimidazoline in an acidic constituent such as Has, 00;,organic aromatic naphtha was pumped continuously 11 down the annulus oithe well at such a rate that one part oi imidazoline was introduced per8,000 parts or oil produced. While thus treating the well, weighed steeltest plates were kept exposed to the well fluids in the tubing and wereperiodically (every two weeks) removed, cleaned and reweighed todetermine the corrosion rate. The initial corrosion rate in this wellbei'ore treatment began was 0.016 inch per year. While treated asdescribed above, the corrosion rate was found to be 0.0005 inch peryear. The rate of imidazoiine injection was then reduced to one part per20,000 parts of oil, and the corrosion rate was iound to be 0.0009 inchper year. The ratio of inhibitor was then increased to one part in 40,000 parts of oil and the corrosion rate rose to, 1 0.003 inch peryear.

Finally, chemical injection was stopped. It was found that after 30 daysthe corrosion rate had risen to 0.013 inch per year and after 60 dayswas again at its original rate, as determined before treatment.

A similar test to the above was run-in a companion well to that used inthe previous test. This well produced 12 bbls. of oil and 2 bbls. ofbrine per day. The brine hadthe same composition as that given above.The well was treated by pouring down the casing once a day a solution ofl-dodecyl,2-methylimidazoline oleate in naphtha. The amount oi solutionused was such as to provide an average concentration of one part of1-dodecyl,2-methylimidazoline per 6,000 parts of oil produced. Thecorrosion rate of steel coupons exposed in the well head was reducedfrom a blank value oi 0.015 inch per year to 0.0015 inch per year.

The protective action of the herein described reagents appears to bemaintained for an appreciable time after treatment ceases, buteventually is lost unless another application is made.

For the protection of gas wells and gas-condensate wells, the amount 01corrosion inhibitor required will usually be within range of one-half to3 lbs. per million cubic feet of gas produced, depending upon theamounts and composition of corrosive agents in the gas and the amount ofliquid hydrocarbon and water produced. However, in no case does theamount of inhibitor required appear to be stoichiometrically related tothe amount of acids produced by a well, since protection is obtainedwith much less imidazoline than usually would be required forneutralization of the acids produced.

Recapitulating, we have found that the cor-- rosion of metals, andparticularly ferrous metals. may be inhibited by the application theretoof a substituted imidazoline in which a substituent at either or boththe 11 or 2-position of the ring contains an aliphatic or cycloaliphatichydrocarbon group having from 8 to 32 carbon atoms. this broad genus ofcorrosion inhibitors, there are several sub-classes which may beemployed effectively in our process. Such sub-classes are, (1) those inwhich the 1-position substituent contains amino group, (2) thosein-which the l-position substituent is free or amino groups, (3) thosein which the 4- and/or 5-position ring carbons are substituted, etc. Theprocess of inhibiting corrosion employing the first of these sub-classesforms the subject-matter or our co-pending application for patent,Serial No. 1,657, filed January 10, 1948,11010 Patent No. 2,446,517,dated Apr. 5, 1949.

Having thus described our invention, what we claim as new and desire tosecure by Letters'Patcut is:

12 1. A process for preventing corrosion of metals, comprising the stepof applying to such metals a substituted imidazoline selected from theclass consisting 01f:

N- CH in which D represents a divalent, non-amino, organic radicalcontaining less than carbon atoms, composed of elements from the groupconsisting of C, H, 0, and N; D represents a- Y metals, comprising thestep oi applying to such metals a substituted imidaaoiine selected fromthe class consisting of in' which D represents a divalent, non-amino,organic radical containing less than 25 carbon atoms, composed ofelements from the group consisting of C, H, 0, and N; D represents adivalent, organic radical containing less than 25 carbon atoms, composedof elements from the group consisting of C, H, O, and N, and containingat least one amino group; and R is a member of the class consisting ofhydrogen and aliphatic and cycloaliphatic hydrocarbon radicals; with theproviso that at least one occurrence of R, contains 8 to 32 carbonatoms.

3. A process for preventing corrosion of ferrous metals, comprising thestep or applying to such metals a substituted imidazoline selected fromthe class consisting of:

in which D represents a divalent, non-amino, or-

ganic radical containing less than 25 carbon atoms, composed of elementsfrom the group consisting of C, H, O, and N; D represents a divalent,

organic radical containing less than 25 carbon I metals, comprising thestep of applying to such metals a substituted imidazoline or thefollowing formula:

N-CHI Ni... l

inwhichltisamemberoitheclassocnsisting 13 of aliphatic andcycloaliphatic hydrocarbon radicals containing to 20 carbon atoms.

5. A process for preventing corrosion of ferrous metals, comprising thestep of applying to such metals a substituted imidazoline of thefollowing formula:

NCH|

\N Hl l metals, comprising the step of applying tosuch metals2-heptadecenylimidazoline.

7. A process for preventing corrosion of ferrous metals, comprising thestep of applying to such metals a substituted imidazoline of thefollowing formula:

N-CH| RC where R is a member of the class consisting of hydrogen andaliphatic and cycloaliphatic hydrol4 inwhich D represents a divalent,non-amino, organic radical containing less than 25 carbon atoms,composed of elements from the group consisting of C, HO, and N; and R isan aliphatic carbon radicals; with the proviso that at least oneoccurrence of R contains 10 to carbon atoms.

8. A process for preventing corrosion of ferrous metals, comprising thestep of applying to such metals a substituted imidazoline of thefollowing formula:

N-CH, a-c

in which R is a member of the class consisting of hydrogen and aliphaticand cycloaliphatic hydrocarbon radicals; with the proviso that at leastone occurrence of R is an aliphatic radical containing from 10 to 20carbon atoms.

9. A process for preventing corrosion of ferrous metals, comprising thestep of applying to such metals l-undecyl, 2-methyl imidazoline.

10. A process for preventing corrosion of ferrous metals, comprising thesteps of applying to such metals a substituted imidazoline of theformula:

N-CH:

- n-c N a in which D represents a divalent, non-amino, organic radicalcontaining less than carbon atoms, composed of elements from the groupconsisting of C, E0, and N; and R is a member of the class consisting ofhydrogen and aliphatic Ri l.

hydrocarbon radical having from 10 to 20 carbon atoms.

12. A process for preventing corrosion of oil and gas well equipment,comprising the step of injecting into the well as substitutedimidazoline selected from the class of:

in which D represents a divalent, non-amino, organic radical containingless than 25 carbon atoms, composed of elements from the groupconsisting of C, H, O, and N; D represents a divalent, organic radicalcontaining less than 25 carbon. atoms, composed of elements from thegroup consisting'of C, H, 0, and N, and containing at least one aminogroup; and R is a member of the class consisting of hydrogen andaliphatic and cycloaliphatic hydrocarbon radicals; with the proviso thatat least one occurrence of R contains 8 to 32 carbon atoms.

13. A process for preventing corrosion of oil and gas well equipment,comprising the step of injecting into the well a substituted imidazolineof the following formula:

in which R is a member of the class consisting of aliphatic andcycloaliphatic hydrocarbon radicals containing 10 to 20 carbon atoms.

14. A process for preventing corrosion of oil and gas well equipment,comprising the step of injecting into the well as substitutedimidazoline of the following formula:

N-CH: R-O

where R is a member of the class consisting oi hydrogen and aliphaticand cycloaliphatic hydrocarbon radicals; with the proviso that at leastone occurrence of R contains 10 to 20 carbon atoms.

15. A process for preventing corrosion of oil and gas well equipment,comprising the step of injecting into the well as substitutedimidazoline of the formula:

R in which D represents a divalent, non-amino, organic radical,containing less than 25 carbon atoms, composed of elements from thegroup car-.- sisting of C, H, O, and N; and R is a member of the classconsisting of hydrogen and aliphat c and cycloaliphatic hydrocarbonradicals; with the proviso that at least one occurrence of R contains 10to 20 carbon atoms.

16. A process for preventing corrosion of oil and gas well equipment,comprising the step of injecting into the well a carboxylic acid salt oiirlm II a mamas imidasoline seiected irom the class at:

' N-cm -cm m-cm N i 1 l 1 \*l' H: \N Ks \l E it l '1, n in which nrepresents a divalent, non-ammo organic radical containing-less thanatoms, composed of elements from the group consisting at C, H, O, and ND represents a divalent. organic radical containing less than 25 carbonatoms, composed of elements from the zroupcomlisting of C, H, O, and N,and containing at least one amino group; and R is a member of the classconsistlna oi hydrogen and aliphatic and cycloaiiphatic hydrocarbonradicals; with the proviso that at least one occurrence of R contains 8to 82 carbon atoms.

17. A process for preventing corrosion of metals, comprising the step ofapplying to such metals a substituted imidazoline selected from theclass consisting of:

N-cB, N-CB: N-CBs N-c& n-d' l 3-4 l n-d l R-d l \N a. N- a. \N B: \N mit in: a

atoms, composedol elementslrcm thegroup con can? . 1Q sisting of C. H,0, and N; D represents a divalent, organic radical containing less than25 carbon atoms, composed of elements from the group consisting of O, H,O, and N, and containing at least oneaminogroumliisamembero] the classconsisting of hydrogen and. aliphatic and cgcloaliphatic hydrocarbonradicals; with the proviso that at least one occurrence of It contains 8to 32 carbon atoms; and B is a member 0! the class consisting ofhydrogen and alkgl radicals having not over two carbon atoms; with theproviso that at least three occurrences of 8 be hydrogen.

CHARLES M. BLAIR, Js.

WILLIAM F. GROSS.

REFERENCES CITED The following references are or record in the tile 0!this patent or the orisinal patent:

. UNITED STA'I'ESPATENTS Number Name Date 1,829,705 walker Oct. 27, 19811,873,084 Walker Aug. 23, 1932 2,357,559 Smith Sept. 5, 1944OTHERREFERENCIB

